Bacillus anthracis is the most frequently used biological warfare agent. During a bioterrorist or biological warfare attack, B. anthracis spores may be dispersed at high concentration into aqueous droplets, which may enter the respiratory tract of humans to cause a lethal infection within 24-48 hours. As B. anthracis is the focus of biological warfare industries, Americans must anticipate the future use of strains that resist antibiotic therapies and that evade the protective immunity of established vaccine programs. An inter-institutional and inter-disciplinary team of scientists developed this Research Project proposal of the Midwestern RCE to test whether genetic determinants that can be demonstrated to be essential for the pathogenesis of anthrax disease can also serve as targets for antiinfective therapy, by either preventing the establishment of an infection or hindering its progression. Natalia Maltsev and colleagues at Argonne National Laboratory exploit the genome sequence of B. anthracis, in addition to all other available information on bacterial pathogenesis, for the computational identification of genes that are essential for the pathogenesis of anthrax. Bioinformatic work will establish an experimental hierarchy, i.e. the order whereby genes in the B. anthracis genome will be examined. Philip Hanna, University of Michigan, and Dominique Missiakas, University of Chicago, will mutate B. anthracis virulence genes and analyze variants for defects in bacterial growth and spore formation. Olaf Schneewind, University of Chicago, will examine the virulence properties of spores generated from B. anthracis variants during animal infection, whereas James Madara, University of Chicago, will analyze spores for defects in the ability to traffic through monolayers of intestinal epithelial cells in vitro. Andrzej Joachimiak, Argonne National Laboratory, will determine the three-dimensional structure and function of B. anthracis virulence factors. Brian Kay, Argonne National Laboratory, will exploit phage-display technologies to isolate peptide ligands of B. anthracis virulence factors. The peptide ligands will be used for the screening of chemical libraries. Compounds that displace peptide ligands from virulence factors will be tested in animal models of infection for therapeutic properties in preventing the onset of anthrax.